While a cellular phone or personal computer having an imaging device has recently become popular, an optical imaging unit used in such a device has been required to be small and yet cover a wide angle of view. A three-lens unit composed of a first lens having a positive refractive power, a second lens having a negative refractive power and a third lens having a positive refractive power, which are arranged in this order from the object side, is known as a small and wide-angle optical unit (see JP-A-2001-75006 (FIG. 1)).
As the disclosure of JP-A-2001-75006 is unsuitable for a reduction in the overall length of the imaging lenses, a still smaller unit has been developed (see JP-A-2004-4566 (FIG. 2)).
In order to make a small and wide-angle unit with two lenses, it has been usual to employ a scratch-resistant glass lens as a first lens 100 on the object side and a second plastic lens 101 behind the first lens 100 and install them in a lens barrel 102, as shown in FIG. 3. The first lens 100 has a small outside diameter and the second lens 101 has a large outside diameter to spread light sharply on the rear side of the first lens 100. Due to the use of the first and second lenses 100 and 101 as described, it has been likely that the forcing of the second lens 101 into the lens barrel 102 may cause moment to occur about the point of its contact with the first lens 100, and that stress may be concentrated on areas designated as A and B in FIG. 3 and cause the second lens 101 to crack or break.